Chapter 2, Problem 2.28E

(a)

Interpretation Introduction

Interpretation:

The structures of the interhalogens along with bond angles have to be predicted.

Concept introduction:

Interhalogens are halogen compounds formed from one heavier and other lighter halogen. The various forms of Interhalogens include $\text{X'X}$, ${\text{X'X}}_3$ and ${\text{X'X}}_5$. Here $\text{X'}$ represents the heavier of the two halogens.

The table that relates the steric number with geometry and bond angles is as follows:

$\begin{array}{cccc}\text{Steric number}& \text{Number of lone pairs}& \text{Molecular geometry}& \text{Bond angles}\\ 2& 0& \text{Linear}& 180°\\ 3& \begin{array}{c}0\\ 1\end{array}& \begin{array}{c}\text{Trigonal planar}\\ \text{Bent}\end{array}& 120°\\ 4& \begin{array}{c}0\\ 1\\ 2\end{array}& \begin{array}{c}\text{Tetrahedral}\\ \text{Trigonal pyramidal}\\ \text{Bent}\end{array}& 109.5°\\ 5& \begin{array}{c}0\\ 1\\ 2\\ 3\end{array}& \begin{array}{c}\text{Trigonal Bi-pyramidal}\\ \text{See-Saw}\\ \text{T-shaped}\\ \text{Linear}\end{array}& 90°\text{,120 }°,180°\\ 6& \begin{array}{c}0\\ 1\\ 2\end{array}& \begin{array}{c}\text{Octahedral}\\ \text{Square pyramidal}\\ \text{Square planar}\end{array}& 90°\text{,}180°\end{array}$

(b)

Interpretation Introduction

Interpretation:

The polar interhalogens amongst $\text{X'X}$, ${\text{X'X}}_3$ and ${\text{X'X}}_5$ has to be identified.

Concept Introduction:

VSEPR model is useful tool to determine shapes as well as properties such as polarity of molecules.

The extent of polarity is quantitatively expressed as dipole moment. It is defined as product of charges of two bonded atoms and the separation between them. The electronegativity difference decides the direction of dipole moment. It is indicated by an arrow head from positive end towards negative end.

(c)

Interpretation Introduction

Interpretation:

The reason behind lighter halogen atom not act as central atom has to be given.

Concept Introduction:

As one moves down the group of halogens, the electronegativity decreases so fluorine is the most electronegative and it is also the lightest amongst all halogens.